1. Field
A condensing type clothes dryer having a heat pump cycle, and a method for controlling a condensing type clothes dryer having a heat pump cycle are disclosed herein.
2. Background
Generally, a clothes dryer is an apparatus for drying laundry by evaporating moisture contained in the laundry, by blowing a hot blast generated by a heater into a drum. The clothes dryer may be classified into an exhausting type clothes dryer and a condensing type clothes dryer according to a processing method of humid air having passed through a drum after drying laundry.
In the exhausting type clothes dryer, humid air having passed through a drum is exhausted outside of the clothes dryer. On the other hand, in the condensing type clothes dryer, humid air having passed through a drum is circulated without being exhausted outside of the clothes dryer. Then, the humid air is cooled to a temperature less than a dew-point temperature by a condenser, so moisture included in the humid air is condensed.
In the condensing type clothes dryer, condensate water condensed by a condenser is heated by a heater, and then heated air is introduced into a drum. While humid air is cooled to be condensed, thermal energy of air is lost. In order to heat the air to a temperature high enough to dry laundry, an additional heater is required.
In the exhausting type clothes dryer, air of high temperature and high humidity should be exhausted outside of the clothes dryer, and external air of room temperature should be introduced to be heated to a required temperature by a heater. As drying processes are executed, air discharged from an outlet of the drum has low humidity. The air is not used to dry laundry, but rather, is exhausted outside of the clothes dryer. As a result, a heat quantity of the air is lost. This may degrade thermal efficiency.
Recently, a clothes dryer having a heat pump cycle, capable of enhancing energy efficiency by collecting energy discharged from a drum and by heating air introduced into the drum using the energy, has been developed.
FIG. 1 is a schematic view illustrating an example of a condensing type clothes dryer having a heat pump cycle. Referring to FIG. 1, the condensing type clothes dryer may include a drum 1 into which laundry may be introduced, a circulation duct 2 that provides a passage such that air circulates via the drum 1, a circulation fan 3 configured to move circulating air along the circulation duct 2, and a heat pump cycle 4 having an evaporator 5 and a condenser 6 serially installed along the circulation duct 2, such that air circulating along the circulation duct 2 passes through the evaporator 5 and the condenser 6. The heat pump cycle 4 may include a circulation pipe, which forms the circulation passage, such that a refrigerant circulates via the evaporator 5 and the condenser 6, and a compressor 7 and an expansion valve 8 installed along the circulation pipe between the evaporator 5 and the condenser 6.
In the heat pump cycle 4, thermal energy of air having passed through the drum 1 may be transferred to a refrigerant via the evaporator 5, and then the thermal energy of the refrigerant may be transferred to air introduced into the drum 1 via the condenser 6. With such a configuration, a hot blast may be generated using thermal energy discarded by the conventional exhausting type clothes dryer or lost in the conventional condensing type clothes dryer.
In the condensing type clothes dryer having a heat pump cycle, in order to increase a heat exchange amount between air and a refrigerant in a heat exchanger, such as an evaporator or a condenser, all components should have a large size. For example, a compressor, the heat exchanger should have a large size, and the amount of refrigerant to be injected should be increased.
In the condensing type clothes dryer having a heat pump cycle, a fin and tube-type heat exchanger is generally used. In a case of the fin and tube-type heat exchanger, a heat exchange amount between air and a refrigerant may be increased as a refrigerant pipe may be divided, and a length of the refrigerant pipe may be extended. However, while the refrigerant pipe may be divided and the length of the refrigerant pipe extended, a pressure loss may occur.
The following formula 1 (Darcy-Weisbach Equation) denotes a pressure loss formula based on friction between the refrigerant pipe and a refrigerant:
                              Δ          ⁢                                          ⁢          P                =                  f          ⁢                      L            D                    ⁢                                    v              2                                      2              ⁢                                                          ⁢              g                                                          (                  Formula          ⁢                                          ⁢          1                )            
where P: Pressure (kgf/cm2), L: Length of pipe (m), f: Friction coefficient, D: Inner diameter of pipe (m), v: Velocity of fluid (m/s), g: Acceleration of gravity (m/s2)
According to formula 1, a pressure loss (ΔP) is increased when a diameter of a refrigerant pipe of an evaporator is reduced, and a length of the refrigerant pipe is increased.
FIG. 2 is a graph comparing pressure-enthalpy (Ph) of the conventional heat pump cycle (comparative example) with pressure-enthalpy (Ph) of a heat pump cycle according to embodiments disclosed herein. As shown in FIG. 2, in the conventional heat pump cycle, when a refrigerant introduced into an evaporator is evaporated, a reduction in pressure occurs, and thus, a pressure loss occurs. This may cause an increase in power consumption due to an additional load of a compressor.